Parlour

Build Status

Parlour is an RBI generator and merger for Sorbet. It consists of two key parts:

  • The generator, which outputs beautifully formatted RBI files, created using an intuitive DSL.

  • The plugin/build system, which allows multiple Parlour plugins to generate RBIs for the same codebase. These are combined automatically as much as possible, but any other conflicts can be resolved manually through prompts.

Usage

There aren't really any docs currently, so have a look around the code to find any extra options you may need.

Using just the generator

Here's a quick example of how you might generate an RBI currently, though this API is very likely to change:

require 'parlour'

generator = Parlour::RbiGenerator.new
generator.root.create_module('A') do |a|
  a.create_class('Foo') do |foo|
    foo.create_method('add_two_integers', [
      Parlour::RbiGenerator::Parameter.new('a', type: 'Integer'),
      Parlour::RbiGenerator::Parameter.new('b', type: 'Integer')
    ], 'Integer')
  end

  a.create_class('Bar', superclass: 'Foo')
end

generator.rbi # => Our RBI as a string

This will generate the following RBI:

module A
  class Foo
    sig { params(a: Integer, b: Integer).returns(Integer) }
    def add_two_integers(a, b); end
  end

  class Bar < Foo
  end
end

Writing a plugin

Plugins are better than using the generator alone, as your plugin can be combined with others to produce larger RBIs without conflicts.

We could write the above example as a plugin like this:

require 'parlour'

class MyPlugin < Parlour::Plugin
  def generate(root)
    root.create_module('A') do |a|
      a.create_class('Foo') do |foo|
        foo.create_method('add_two_integers', [
          Parlour::RbiGenerator::Parameter.new('a', type: 'Integer'),
          Parlour::RbiGenerator::Parameter.new('b', type: 'Integer')
        ], 'Integer')
      end

      a.create_class('Bar', superclass: 'Foo')
    end
  end
end

(Obviously, your plugin will probably examine a codebase somehow, to be more useful!)

You can then run several plugins, combining their output and saving it into one RBI file, using the command-line tool. For example, if that code was in a file called plugin.rb, this would save the RBI into output.rbi:

parlour --relative-requires plugin.rb MyPlugin output.rbi

You can also use plugins from gems. If that plugin was published as a gem called parlour-gem:

parlour --requires parlour-gem MyPlugin output.rbi

The real power of this is the ability to use many plugins at once:

parlour --requires gem1,gem2,gem3 Gem1::Plugin Gem2::Plugin Gem3::Plugin output.rbi

Code Structure

Overall Flow

                        STEP 1
                 All plugins mutate the
                 instance of RbiGenerator
                 They generate a tree
                 structure of RbiObjects

                 +--------+  +--------+
                 |Plugin 1|  |Plugin 2|
                 +----+---+  +----+---+         STEP 2
                      ^           ^        ConflictResolver
                      |           |        mutates the structure
+-------------------+ |           |        to fix conflicts
|                   | |           |
| One instance of   +-------------+        +----------------+
| RbiGenerator      +--------------------->+ConflictResolver|
|                   |                      +----------------+
+---------+---------+
          |
          |
          |          +-------+          STEP 3
          +--------->+ File  |    The final RBI is written
                     +-------+    to a file

Generation

Everything that can generate lines of the RBI implements the RbiGenerator::RbiObject abstract class. The function generate_rbi accepts the current indentation level and a set of formatting options. (Each object is responsible for generating its own indentation; that is, the lines generated by a child object should not then be indented by its parent.)

I think generation is quite close to done, but it still needs features like constants and type parameters.

Plugins

Plugins are automatically detected when they subclass Plugin. Plugins can then be run by passing an array of them, along with an RbiGenerator, to Plugin.run_plugins. Once done, the generator will be populated with a tree of (possibly conflicting) RbiObjects - the conflict resolver (detailed below) will clear up any conflicts.

Conflict Resolution

This is a key part of the plugin/build system. The ConflictResolver takes a namespace from the RbiGenerator and merges duplicate items in it together. This means that many plugins can generate their own signatures which are all bundled into one, conflict-free output RBI.

It is able to do the following merges automatically:

  • If many methods are identical, delete all but one.
  • If many classes are defined with the same name, merge their methods, includes and extends. (But only if they are all abstract or all not, and only if they don't define more than one superclass together.)
  • If many modules are defined with the same name, merge their methods, includes and extends. (But only if they are all interfaces or all not.)

If a merge can't be performed automatically, then the #resolve_conflicts method takes a block. This block is passed all the conflicting objects, and one should be selected and returned - all others will be deleted. (Alternatively, the block can return nil, and all will be deleted.) This will allow a CLI to prompt the user asking them what they'd like to do, in the case of conflicts between each plugin's signatures which can't automatically be resolved.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/AaronC81/parlour. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Parlour project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.